Neurourological Research in a Total LabVIEW Environment

Author(s):
Paul Dolber - Aegis Solutions, Inc.
Karl Thor - Eli Lilly and Company
Ronald Bremer - Durhan Veterans Affairs Medical Center
Amit Rupani - Duke University Medical Center

Industry:
Biotechnology

Products:
Compact FieldPoint, LabVIEW, FieldPoint

The Challenge:
Develop equipment and user-modifiable software to enable comprehensive study of the neural control of the lower urinary tract by both noninvasive and invasive techniques.

The Solution:
Fabrication of a behavioral micturition recording system using National Instruments FieldPoint hardware and LabVIEW software, and of cystometry and in vitro contractility systems using a National Instruments data acquisition board and LabVIEW software.

Introduction

Proper operation of the lower urinary tract (LUT) depends on the synchronized function of several muscles (especially urinary bladder smooth muscle and pelvic floor striated muscle) and a variety of nerve cells and neurotransmitters regulating those muscles. LUT control is complex, involving the interplay of neurons at many different levels of the nervous system. Moreover, the anatomical and functional characteristics of both nerve and muscle tissue change in many pathophysiological states, including prostatic enlargement, diabetes, stroke, and aging, and thereby results in symptoms including incontinence and the urgent need to urinate frequently. To understand LUT regulation, we must study it in both normal and pathological states, and assess the influence of pharmacological agents and of nerve stimulation. Three prominent experimental modalities are the behavioral study of micturition (determining the frequency and volume of micturition in conscious unrestrained rats), cystometry (measuring bladder pressure, micturition volume, and urinary frequency), and in vitro contractility (studying mechanical behavior of isolated bladder muscle strips). To perform these studies, we assembled systems utilizing National Instruments data acquisition hardware controlled by LabVIEW software.

Chronic micturition recording system

Micturition behavior is established over a period of two to three days using a chronic micturition recording system (CMRS) of our design. Rats are housed in a set of eight large "metabolic" cages with collection into separate cylindrical collectors. Each collector is connected by tubing on one side to pressure transducers mounted at the height of the bottom of the collection tube, and on the other side to pinch valves which ordinarily isolate the collector from room vacuum. Urine accumulation results in an increase in pressure transducer current output.

The LabVIEW program we wrote to control this system accomplishes several different tasks. First, transducer output is examined graphically to assess transducer performance. Second, the relationship between fluid volume and transducer output is used to calibrate the system. Third, transducer output is monitored once every 30 sec using a FieldPoint analog input module and converted to micturition volume using the calibration data. Fourth, if the change in volume since the preceding 30 sec period is greater than a threshold value of 0.05 ml (roughly one drop), the time and the micturition volume are recorded in a text file. Additionally, the occurrence of a micturition event is graphically recorded on the monitor, one cage at a time. Fifth, because a large rat can void more volume during the evening hours than sensitive collection devices can hold, we later incorporated a subVI which every few hours pauses the program, uses a FieldPoint discrete output module to serially open pinch-valves connecting each collector to vacuum lines through which they are emptied, and appropriately resets the current reading. Thus, the rats can be left undisturbed for many hours. The modular nature of the FieldPoint hardware greatly simplified the addition of the pinch-valve control system.

Cystometry and in vitro contractility

For cystometry, a catheter is inserted through the top of the bladder to allow input of fluid and simultaneous monitoring of pressure, while voided urine is automatically collected into a tube suspended from a force transducer. Transducer outputs are directed through a shielded BNC-2090 adaptor chassis into a PCI-MIO-16XE-10 data acquisition board in a 400 MHz PC clone. Because the events of interest occur rather slowly our sampling rate is kept low at 20-50 Hz. The program used for data acquisition ("cystometry logger") is substantially modified from one generated using DAQ Solution Wizard. At our low sampling rate, it is feasible to send the data both to a binary file (in part because the experiments are often up to 10 hrs long) and to a front-panel chart displaying 15 min of data at a time. Entered comments are time-stamped and saved to a separate text file. After cystometry is complete, another program ("interval reader," also modified from one generated using DAQ Solution Wizard) is used to play back the data. The data can be viewed one channel at a time to allow for measurement of waveform characteristics with cursors (with data being sent to a spreadsheet file). They can also be viewed together, with the graphs being sent to a printer, or with the data used in the graph being sent to other spreadsheet files. Because the number of data points over long time intervals may greatly exceed the number needed for a good plot of the data, we included a front-panel "decimation selector" to select only every nth  point for display.

Slightly modified versions of these programs are used for in vitro contractility studies. Small strips of bladder muscle kept in saline in eight organ baths are connected to strain gauges to measure contractile force. During exposure to pharmacological agents or to electrical stimulation of the nerves supplying the muscle, the force generated is monitored using the strain gauge amplifiers which are directed through the BNC-2090 into the PCI-MIO-16XE-10. The heterogeneous behavior of the strips, all from the same animal, and their variable response to norepinephrine, is a conspicuous feature of obstructed bladder muscle.

Conclusions

National Instruments hardware and LabVIEW software have proven to be extremely useful in the execution of our complimentary behavioral, in situ cystometric, and in vitro contractility experiments. A very important feature of the LabVIEW environment is that all of the programs are easily maintained in-house by the end users. Although the users have little programming experience, they easily succeed in modifying the programs as required by changes in experiment design.

 

 

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